燃煤初期“碳烟-矿物质”相互作用对超细颗粒物演化的影响研究

The Impact of Soot-Minerals Interaction on the Early-Stage Ultrafine Particulate Matter Evolution in Coal Combustion

煤粉燃烧初期阶段碳烟与矿物质的相互作用对超细颗粒物演化的影响亟待阐明。本文基于颗粒群平衡模型,实现了碳烟"生成-氧化"及Na_2O-SiO_(2)体系"热解-核化-聚并"机理的模型耦合,研究了低阶煤准东煤燃烧初期超细颗粒物的演化特性。耦合模型预测的超细颗粒物粒径分布与实验测量数据吻合较好。结果表明,在1200 K和1500 K下,准东煤燃烧过程中碳烟单体、Na_(2)O单体和SiO_(2)单体的生成均具有十分相近的时间尺度(0.01~0.03 s)。因此,燃烧初期碳烟和矿物质的相互作用(主要是碰撞聚并过程)对超细颗粒物的粒径分布具有显著影响。而当停留时间超过0.1 s,碳烟占比达峰后大量氧化,导致碳质组分在超细颗粒物中的占比不断下降(低于13%),此后超细颗粒物粒径分布的演化则由矿物质组分来决定。

The impact of soot-minerals interaction on the ultrafine particulate matter(PM)evolution in the pulverized coal combustion largely remains unclear.This paper intensively incorporates the soot formation-oxidation model with the volatilization—nucleation—coagulation mechanism of the Na_(2)O-SiO_(2) system,yielding an integrated population balance model for the investigation of ultrafine PM evolution in the early-stage combustion of the low-rank Zhundong coal.The predicted ultrafine particle size distribution(PSD)agrees reasonably well with the experiments.It is revealed that,in burning Zhundong coal,the primary soot coincides with Na_(2)O and SiO_(2) monomers on their forming time scales(〜1 ms)under either 1200 K or 1500 K.Thus,the soot-minerals interaction,mainly through coagulation,has a prominent effect on the early-stage ultrafine PSD.After the residence time exceeds 0.1 s,the mass fraction of soot in the ultrafine PM drops rapidly from the peak value due to massive soot oxidation.With carbonaceous fraction lower than 13%,the ensuing PSD evolution of ultrafine PM is dominated by the mineral species of coal.